RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.
G2A - Enjoy the vast offer of Steam, Origin, Uplay, Battle.net, GOG, PSN and XBOX CD-Keys at the most attractive prices on the market. Don’t overpay – buy cheap on G2A.COM!
Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.
Green Man Gaming - A digital distributor for video games.
Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything
GOG.com - DRM-free game store, selling both new and old titles. No clients required.